1. Field of the Invention
The invention relates to compositions for improving the appearance of skin, particularly to provide good coverage over imperfections such as pores and uneven skin tone, while retaining a natural skin appearance.
2. The Related Art
A matte effect is often sought from facially applied cosmetics. The matte finish overcomes the shiny effect engendered by greasy skin, particularly under hot and humid conditions. Absorbent fillers such as talc, silica, kaolin and other inorganic particulates have been used to achieve the effect by their optical properties.
Imperfect skin can be hidden in two ways through manipulation of light transmission. In the first, components of the cosmetic may simply reflect light back toward the source. An alternative approach is referred to as achieving a soft focus effect. Here the incoming light is distorted by scattering (lensing). Components of the color cosmetic in this mechanism operate as lenses to bend and twist light into a variety of directions.
While it is desirable to hide imperfect skin through a matte effect, there is also a desire to achieve a healthy skin radiance. A cosmetic covering that is too opaque hides the skin under a paint-like coating. Imperfections are hidden but there is no radiance. Some refer to this as whitening. Where light transmission is insufficiently hindered, the opposite occurs. Here the glow may be healthy but aesthetically displeasing skin topography and color may now be apparent.
U.S. Pat. No. 5,997,890 (Sine et al.), U.S. Pat. No. 5,972,359 (Sine et al.), and U.S. Pat. No. 6,174,533 B1 (SaNogueira, Jr.) are all directed to topical compositions to provide good coverage of skin imperfections. The solution proposed by these documents is the use of a metal oxide with a refractive index of at least about 2 and a neat primary particle size of from about 100 to about 300 nm. Preferred particulates are titanium dioxide, zirconium oxide and zinc oxide.
A significant disadvantage of titanium dioxide and zinc oxide is the whitening effect upon the skin. An undesirable ashen appearance is unfortunately created.
U.S. patent application Ser. No. 2005/0163813 A1 (Kosbach et al.) reports use of fumed alumina particles for enhancing the soft-focus effect of certain cosmetic compositions. Levels of at least 3% are required to accomplish effective light diffusing properties to disguise skin imperfections.
Crosslinked silicone elastomers have been identified as aids in achieving soft focus. U.S. patent application Ser. No. 2005/0163730 A1 (Rosevear et al.) discloses a synergistic interaction between crosslinked silicone elastomer and zinc oxide having average particle size less than 300 nm. A related disclosure is found in U.S. patent application Ser. No. 2005/0249684 A1 (Dobkowski et al.) wherein a taurate polymer enhances optical effects in combination with a silicone elastomer and zinc oxide.
A disadvantage of silicone elastomers is their incompatibility with water. These materials are also difficult to disperse within aqueous emulsions at relatively high concentration levels of the elastomer.
Therefore, the challenge remains to provide a soft focus effect which avoids the whitening phenomena and also has good compatibility with water or at least water and oil emulsions.